Micro-Drilling of ZTA and ATZ Ceramic Composit: Effect of Cutting Parameters on Surface Roughness

Ceramics are a class of materials widely used during last fifteen years for orthopaedic applications. It is well known that they are characterized by low wear rate, and friction coefficient. However, these materials are very difficult to machine into complex shapes because of their brittleness and high hardness. The most effective method to increase the crack resistance is the formation of a composite structure. This class of materials, composed by two or more different ceramics, can present higher characteristic respect to the single component, like fracture toughness and flexural strength. This paper presents a study of the influence of cutting parameters (cutting speed, feed rate and step number) onto the hole surface roughness and deformation due to the drill operation. The ceramic composite materials AZT (alumina toughened zirconia) and ZTA (zirconia toughened alumina) were first characterized in terms of hardness and roughness. After the drilling test, the holes were analyzed using scanning electron microscope (SEM) and an advanced 3-dimensional non-contact optical profilomete

Using small-angle X-ray scattering to investigate the compaction behaviour of a granulated clay

The compaction behaviour of a commercial granulated clay (magnesium aluminium smectite, gMgSm) was investigated using macroscopic pressure-density measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray microtomography (XμT) and small-angle X-ray scattering (SAXS). This material was studied as a potential compaction excipient for pharmaceutical tabletting, but also as a model system demonstrating the capabilities of SAXS for investigating compaction in other situations. Bulk compaction measurements showed that the gMgSm was more difficult to compact than polymeric pharmaceutical excipients such as spheronised microcrystalline cellulose (sMCC), corresponding to harder granules. Moreover, in spite of using lubrication (magnesium stearate) on the tooling surfaces, rather high ejection forces were observed, which may cause problems during commercial tabletting, requiring further amelioration. Although the compacted gMgSm specimens were more porous, however, they still exhibited acceptable cohesive strengths, comparable to sMCC. Hence, there may be scope for using granular clay as one component of a tabletting formulation. Following principles established in previous work, SAXS revealed information concerning the intragranular structure of the gMgSm and its response to compaction. The results showed that little compression of the intragranular morphology occurred below a relative density of 0 · 6, suggesting that granule rearrangements or fragmentation were the dominant mechanisms during this stage. By contrast, granule deformation became considerably more important at higher relative density, which also coincided with a significant increase in the cohesive strength of compacted specimens. Spatially-resolved SAXS data was also used to investigate local variations in compaction behaviour within specimens of different shape. The results revealed the expected patterns of density variations within flat-faced cylindrical specimens. Significant variations in density, the magnitude of compressive strain and principal strain direction were also revealed in the vicinity of a debossed feature (a diametral notch) and within bi-convex specimens. The variations in compaction around the debossed notch, with a small region of high density below and low density along the flanks, appeared to be responsible for extensive cracking, which could also cause problems in commercial tabletting

Effects of operating and geometric variables on hydrodynamics and tablet dissolution in standard and modified dissolution testing apparatuses 2

Dissolution testing is routinely conducted in the pharmaceutical industry to provide critical in vitro drug release information for quality control purposes, and especially to assess batch-to-batch consistency of solid oral dosage forms such as tablets. Among the different types of apparatuses listed in the United States Pharmacopoeia (USP), the most commonly used dissolution system for solid dosage forms is the USP Dissolution Testing Apparatus 2, consisting of an unbaffled, hemispherical-bottomed vessel equipped with a 2-blade radial impeller. Despite its extensive use in industry and a large body of work, some key aspects of the hydrodynamics of Apparatus 2 have received very little attention, such as the determination of its power dissipation requirements (which controls solid-liquid mass transfer processes) and the velocity distribution under the different agitation conditions at which this system is routinely operated. In addition, the tablet dissolution performance of Apparatus 2 has been shown to be highly sensitive to a number of small geometric factors, such as the exact locations of the impeller and the dissolving tablet. Therefore, in this study, computation and experimental work was conducted to (a) quantify the roles of some key hydrodynamic variables of importance for the standard Apparatus 2 system and determine their impact on the dissolution profiles of solid dosage forms, and (b) design and test a modified Apparatus 2 that can overcome the major limitations of the standard system, and especially those related to the sensitivity of the current apparatus to tablet location. Accordingly, the hydrodynamics in the standard USP Apparatus 2 vessel was experimentally quantified using Laser-Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV). Complete experimental mapping of the velocity distribution inside the standard Apparatus 2 was obtained at three agitation intensities, i.e., 50 rpm (NRe=4939), 75 rpm (NRe= 7409) and 100 rpm (NRe= 9878). The velocity distributions from both LDV and PIV were typically found to be very similar. It was found that the overall flow pattern throughout the whole vessel was dominated by the tangential component of the velocity at all agitation speeds, whereas the magnitudes of the axial and radial velocity components were typically much smaller. In the bottom zone of the vessel, two regions were observed, i.e., a central, low-velocity inner core region, and an outer recirculation loop below the impeller, rotating around the central inner core region. This core region typically persisted, irrespective of the impeller agitation speed. Computation Fluid Dynamics (CFD) was additionally used to predict velocity profiles. Typically, the CFD predictions matched well the experimental results. The power dissipated by the impeller in Apparatus 2 was experimentally measured using a frictionless system coupled with torque measurement. CFD was additionally used to predict the power consumption, using two different approaches, one based on the integration of the local value of the energy dissipation rate, and the other based on the prediction of the pressure distribution on the impeller blade, from which the torque and the power required to rotate the impeller were predicted. The agreement between the experimental data and both types of numerical predictions was found to be quite satisfactory in most cases. The results were expressed in terms of the non- dimensional Power number, Po, which was typically found to be on the order of ~0.3. The power number was observed to decrease very gradually with increasing agitation speeds. The results of this work and of previous work with the standard USP Apparatus 2 confirm that this apparatus is very sensitive to the location of the tablet, which is typically not controlled in a typical test since the tablet is dropped into the vessel at the beginning of the test and it may rest at random locations on the vessel bottom. Therefore, in this work a modified USP Dissolution Testing Apparatus 2, in which the impeller was placed 8-mm off-center in the vessel, was designed and tested. This design eliminates the poorly mixed inner core region below the impeller observed in the standard Apparatus 2 vessel. Dissolution tests were conducted with the Modified Apparatus for different tablet locations using both disintegrating calibrator tablets (Prednisone) and non-disintegrating calibrator tablets (Salicylic Acid). The experimental data clearly showed that all dissolution profiles in the Modified Apparatus were not affected by the tablet location at the bottom of the vessel. This design can effectively eliminate artifacts generated by having the tablet settle randomly at different locations on the vessel bottom after dropping it at the beginning of a dissolution testing experiment. The hydrodynamic and mixing characteristics of the modified Apparatus 2 were studied in some detail by experimentally measuring and computationally predicting the velocity distribution, power dissipation, and mixing time in the modified system. The velocity profiles near the bottom of the vessel were found to be significantly more uniform than in the standard Apparatus 2, because of the elimination of the poorly mixed zone below the impeller. The power dissipation in the modified Apparatus 2 was typically higher than in the standard system, as expected for an non-symmetrical system, and the corresponding Power number, Po, was less dependent on Reynolds number than Po in the standard system. Finally, the mixing time in the modified system, as experimentally measured by using a decolorization method and computationally predicted through CFD simulation, was found to be shorter in the modified Apparatus 2 by 7.7 %-12.9 % as compared to Apparatus 2. It can be concluded that the modified Apparatus 2 is a more robust testing apparatus, which is capable of producing dissolution profiles that are less sensitive to small geometric factors that play a major role in the standard USP Apparatus 2

Surface temperature mapping with infrared photographic pyrometry for turbine cooling investigations

Surface temperature mapping with infrared photographic pyrometry for turbine cooling investigation

Comparison of engagement and emotional responses of older and younger adults interacting with 3D cultural heritage artefacts on personal devices

The availability of advanced software and less expensive hardware allows museums to preserve and share artefacts digitally. As a result, museums are frequently making their collections accessible online as interactive, 3D models. This could lead to the unique situation of viewing the digital artefact before the physical artefact. Experiencing artefacts digitally outside of the museum on personal devices may affect the user's ability to emotionally connect to the artefacts. This study examines how two target populations of young adults (18–21 years) and the elderly (65 years and older) responded to seeing cultural heritage artefacts in three different modalities: augmented reality on a tablet, 3D models on a laptop, and then physical artefacts. Specifically, the time spent, enjoyment, and emotional responses were analysed. Results revealed that regardless of age, the digital modalities were enjoyable and encouraged emotional responses. Seeing the physical artefacts after the digital ones did not lessen their enjoyment or emotions felt. These findings aim to provide an insight into the effectiveness of 3D artefacts viewed on personal devices and artefacts shown outside of the museum for encouraging emotional responses from older and younger people

On-line Handwritten Character Recognition: An Implementation of Counterpropagation Neural Net

On-line handwritten scripts are usually dealt with pen tip traces from pen-down to pen-up positions. Time evaluation of the pen coordinates is also considered along with trajectory information. However, the data obtained needs a lot of preprocessing including filtering, smoothing, slant removing and size normalization before recognition process. Instead of doing such lengthy preprocessing, this paper presents a simple approach to extract the useful character information. This work evaluates the use of the counter- propagation neural network (CPN) and presents feature extraction mechanism in full detail to work with on-line handwriting recognition. The obtained recognition rates were 60% to 94% using the CPN for different sets of character samples. This paper also describes a performance study in which a recognition mechanism with multiple hresholds is evaluated for counter-propagation architecture. The results indicate that the application of multiple thresholds has significant effect on recognition mechanism. The method is applicable for off-line character recognition as well. The technique is tested for upper-case English alphabets for a number of different styles from different peoples

Characterization of low thermal conductivity PAN-based carbon fibers

The microstructure and surface chemistry of eight low thermal conductivity (LTC) PAN-based carbon fibers were determined and compared with PAN-based fibers heat treated to higher temperatures. Based on wide-angle x ray diffraction, the LTC PAN fibers all appear to have a similar turbostratic structure with large 002 d-spacings, small crystallite sizes, and moderate preferred orientation. Limited small-angle x ray scattering (SAXS) results indicate that, with the exception of LTC fibers made by BASF, the LTC fibers do not have well developed pores. Transmission electron microscopy shows that the texture of the two LTC PAN-based fibers studied (Amoco T350/23X and /25X) consists of multiple sets of parallel, wavy, bent layers that interweave with each other forming a complex three dimensional network oriented randomly around the fiber axis. X ray photoelectron spectroscopy (XPS) analysis finds correlations between heat treated temperatures and the surface composition chemistry of the carbon fiber samples